1. Field of the Invention
The present invention relates to a composition of matter comprising an alloy having a high vibrational damping capacity and, in another aspect, to a disk drive actuator suspension arm comprised of the alloy.
2. Prior Art
At the present time, most computer systems store data on a disk drive. A disk drive includes inter alia a rotatable disk, and an actuator that moves a transducer over the surface of the disk. The transducer element is normally disposed within a small ceramic body affixed to a pivotally mounted load beam. In operation, in order for the transducer to sustain a transducing relationship with the disk, the transducer xe2x80x9cflysxe2x80x9d over the surface of the disk at an elevation of less than 0.001 mm. Electronic circuitry and servo-motor means enable the transducer to write data on, and read data from, a selected portion of the disk surface.
The high rotational speed of the disk creates fluid turbulence (or windage) in the volume of air adjacent thereto. This turbulence may impart a force upon the loadbeam, driving a resonant response. During operation, the loadbeam may be subjected to sudden acceleration due to actuator arm contact with travel-limiting xe2x80x9ccrashxe2x80x9d stops. This contact may also initiate a resonant response in the loadbeam. In addition, the forces of acceleration, accompanying normal disk drive data-seeking operations, may generate a resonant response in the loadbeam. Non-repeatable runout (NRR) of the disk, coupled with the loadbeam""s attempt to follow these eccentricities, may result in a resonant response. Disk drives sometimes operate in hazardous environments that may include being dropped from several inches. Such shock loads, when experienced during disk operation, may drive a resonant response in the loadbeam. Notwithstanding these excitations, the load beam, and the transducer attached thereto, must maintain the transducing relationship between the transducer and the surface of the disk at all times. If the resonant vibrations are not damped promptly and effectively, the elevational excursions of the load beam may cause damage to the surface of the disk, the transducer and/or the load beam, or the lateral excursions of the load beam may cause data track mis-registration and read-write errors. It is, therefore, desirable to provide a load beam, mounting arm and/or flexure having a high damping capacity.
Material damping occurs when repetitive deformation (vibration) of a material is dissipated through internal energy losses, usually in the form of heat. There are two basic types of damping behavior: inelastic and hysteretic. Inelastic damping occurs when there is a lag between the application of a stress and the resulting equilibrium value of the strain that is frequency and temperature dependent. Mechanisms that give rise to this type of damping, in metals, include the interaction of specific point defects with other point defects or dislocations, precipitation phenomena, and ordering effects.
Hysteretic damping, as used herein, is defined as frequency independent loss. Hysteretic damping materials exhibit a stress-strain behavior on loading that does not retrace the behavior on unloading. The area difference between the loading and unloading curves is then proportional to the energy loss for the material. While hysteretic damping is independent of frequency it is dependent on the applied stress (or strain amplitude). Materials that exhibit hysteretic damping are the preferred materials for applications where noise and vibration reduction are desired. Hysteretic damping occurs through boundary motion, for example, the motion of magnetic domains in ferromagnetic materials (magnetoelastic behavior) and the motion of twin boundaries (thermoelastic behavior).
The damping capacities of various metals are shown in FIG. 1. Exemplary of materials having excellent damping capacity are xe2x80x9cshape memoryxe2x80x9d alloys such as NiTi (Nitinols), cast Mnxe2x80x94Cu alloys (Sonotron), and polymer matrix composites. Fe-based materials, other than pure Fe, exhibiting the highest specific damping capacity are Fexe2x80x94Cr alloys, cast irons, and ferritic stainless steels. Fexe2x80x94Crxe2x80x94Al, ferritic stainless alloys (known as xe2x80x9cSilentalloyxe2x80x9d) are reported to be high damping structural materials and were developed for use in corrosive environments. This type of alloy would would be ideal for fabricating a load beam for a disk drive actuator, meeting almost all requirements except for the fact that these materials are ferritic and thus, ferromagnetic. There is, therefore, a continuing need for a high damping, substantially non-magnetic material for use in disk drive actuator assemblies.
A high-damping, corrosion resistant and substantially non-magnetic material for a disk drive suspension arm and load beam having high damping properties is disclosed. A disk drive assembly includes a disk having a readable and writeable surface, a motor operable for rotating the disk, and an actuator assembly that includes a transducer mounted on a load beam. The actuator assembly is operable for positioning the transducer in transducing relationship with the surface of the disk.
The high rotational speed of the disk creates fluid turbulence (or windage) in the volume of air adjacent thereto. Such turbulence may impart a force upon the loadbeam, driving a resonant response. During operation, the loadbeam may be subjected to sudden acceleration due to actuator arm contact with travel- limiting xe2x80x9ccrashxe2x80x9d stops. This contact may also initiate a resonant response in the loadbeam. The forces of acceleration resulting from normal disk drive data-seeking operations may generate a resonant response in the loadbeam. Non-repeatable runout (NRR) of the disk, coupled with the loadbeam""s attempt to follow these eccentricities, may result in a resonant response within the loadbeam. Disk drives occasionally operate in hazardous environments that mayinclude being dropped from several inches. Such operating shock loads may drive a resonant response in the loadbeam. Notwithstanding these excitations, the load beam, and the transducer attached thereto, must maintain the transducing relationship between the transducer and the surface of the disk at all times. If the resonant vibrations are not damped promptly and effectively, the elevational excursions of the load beam may cause damage to the surface of the disk, the transducer and/or the load beam or result in data track mis-registration and read-write errors. It is, therefore, desirable to provide a load beam, or any similar flexure used in a disk drive, having a high damping capacity.
The present invention discloses alloy compositions of the form (14-20)Mn, (10-13)Cr, (0-6)Si, (4-10)Ni, (0-6)Co, and (0-0.2)N, the components being present in the range of percentages indicated with the balance being Fe. A preferred embodiment of the present invention is an alloy consisting essentially of Fe-15Mn-12Cr-3Co-3Ni-0.1N. The alloy has stainless steel-type properties and exhibits high damping characteristics. The alloy, which has both an austentitic and a ferrite phase, can be melted, cast and rolled into sheets. Disk drive load beams cut from the alloy sheet exhibit higher vibrational damping than materials currently used in the art.
It is an overall object of the invention to provide a composition of matter that is substantially non-magnetic and can be shaped to form a body characterized by, in combination, a high strength to weight ratio and a high vibrational damping capacity.
It is a particular object of the invention to provide an alloy which is suitable for fabricating a suspension mounting arm, loadbeam and/or flexure for a computer disk drive which meets the requirements demanded by the application. An exemplary list of typical specifications setting forth the requirements for a material suitable for use in manufacturing a suspension arm include:
1. be capable of being welded to 302/304 stainless steel;
2. have a high a strength to weight ratio;
3. be substantially non-magnetic;
4. be corrosion resistant;
5. have good internal damping properties to mute resonance modes given a forced impulse input;
6. be resilient and stable under dynamic load (up to 2500 g""s) and heat (200xc2x0 F.);
7. be formable into a sheet which preferably leaves little or no burr when sheared at a cutting clearance of 5% of material thickness;
8. does not cause excessive wear (with light lubrication) on tooling and other components used during normal stamping operations;
9. have an attractive, consistent, unblemished luster or matte finish. Ra less than 31xcexcin;
10. not out-gas, flake or otherwise generate contamination when sealed in a disk drive for up to 15 years.
The most commonly used austenite stainless steel meets the performance criteria of 1, 3, 4, 8, 9, and 10. It is, therefore, a particular object of the present invention to provide a material for a disk drive suspension arm assembly having improved characteristics over austentitic stainless steel with respect to requirements numbered 2, 5, 6 and 7 above.
It is a further object of the invention to provide an alloy meeting the above objective and that, in addition, can be rolled into a sheet and shaped by a stamping machine.
It is yet a further object of the invention to provide an alloy that can be formed into a sheet that can be sheared by a stamping tool at a cutting clearance of 5% of the sheet thickness without leaving a burr.
The features of the invention believed to be novel are set forth with particularity in the appended claims. However the invention itself, both as to organization and method of operation, together with further objects and advantages thereof may be best be understood by reference to the following description of the invention in conjunction with the accompanying drawings.